The overall objectives are to (1) probe the structure of ligandin (glutathione-S-transferase B) to determine how this protein accomplishes its catalytic and binding functions; (2) explore the structure and expression of ligandin gene(s). The specific aims of studies dealing with the structural aspects of ligandin are to: (1) determine the effect of selective chemical modification on the catalytic and binding properties of ligandin; (2) isolate the catalytic and binding site peptides; (3) determine if the carcinogen binding site is identical to other binding or catalytic sites; (4) determine if Yb (25K) subunit could be a precursor to Ya (22K) subunit and (5) determine which subunit has glutathione peroxidase activity and if this activity is inhibited by bilirubin, sulfobromophthalien, steroids and substrates of glutathione-S-transferase activity. The specific aims of the studies dealing with molecular aspects are to use our ligandin cDNA probe to: (1) quantitate mRNA for ligandin subunits during development, in liver, kidney and gonads in male and female rats; (2) compare the size of ligandin mRNA in nucleus and cytoplasm; (3) determine the number of ligandin gene copies and examine the possible existence of separate genes for the two subunits; (4) determine if there is altered degree of methylation in ligandin gene in hepatoma; (5) select the genomic clones of ligandin from the genomic clone libraries, and; (6) determine if there are intervening sequences in ligandin gene by R-looping with genomic DNA and comparative restriction mapping of cDNA and genomic DNA. Since ligandin is important in detoxification, carcinogenesis and net uptake of several organic anions from the blood by the liver, the proposed studies will help in understanding the molecular mechanisms involved in these biological processes. These studies may also provide insights into molecular mechanisms involved in tissue specific synthesis of subunits of oligomeric enzymes.